Computer-based health information exchange (HIE) projects are being developed throughout the country to improve the safety, quality and efficiency with which health care is delivered, and to create the building blocks of a nationwide health information network (NHIN) as called for by President George W. Bush and the Department of Health and Human Services. Although it is expected that the electronic exchange of clinical data among disparate providers will improve clinical care, there are few direct data showing its utility. The project described here seeks to evaluate the impact of an HIE project on the quality, safety and cost of clinical care provided in New York metropolitan area. An evaluation showing the benefits of HIE in this diverse and densely populated region would be a significant step toward building a body of knowledge that discusses and supports the use of HIE. The specific hypothesis behind the proposed evaluation plan is that the implementation of a computerbased HIE network in the New York metropolitan area will improve the quality and safety and decrease the cost of health care delivery, while being met with a high degree of provider satisfaction. This hypothesis is based on the following observations. First, information gaps exist for clinicians at the bedside that likely lead to errors and a reduction in the quality and safety of the health care they deliver, and these gaps would be significantly improved by HIE. Second, in limited instances access to clinical data through HIE has been shown to increase efficiency and save money, and is projected to save billions of dollars annually if implemented nationwide. Third, there is a perceived need among emergency physicians in the New York metropolitan area for computer-based HIE and therefore an implementation in this region is likely to elicit a high degree of user satisfaction. The specific aims of this study are to: 1. Evaluate the impact on quality and safety of an HIE application implemented in ten emergency departments in the New York metropolitan area. 2. Evaluate the return on investment for an HIE application implemented in ten emergency departments in the New York metropolitan area from the perspectives of both providers and payers. 3. Evaluate provider satisfaction with the HIE application in ten emergency departments in the New York metropolitan area.